DESCRIPTION (adapted from the application) Autosomal dominant polycystic kidney disease (ADPKD) is a common inherited disorder with a number of systemic manifestations including renal cysts, hepatic cysts and cerebral aneurysms. The gene for the most common form of the disease, PKD1, has been cloned and sequenced and is predicted to encode a protein with a novel combination of functional motifs that may be involved in cell-cell/matrix signaling. It has not been possible to confirm the protein's putative structure by the isolation of full-length cDNAs and preliminary studies by the applicant have suggested that transcripts from this gene may be more complex than initially thought. Specifically, we have identified two area of alternative splicing. The first is located in the 5' end of the gene and appears to exhibit tissue specific differences while the second, located in th vicinity of an unusual polypyrimidine tract in the middle of the gene, yields novel pattern of semi-random splicing. This latter pattern is predicted to result in a population of truncated proteins that mimics the effect of previously reported germline mutations. This application seeks to characterize splicing patterns of the PKD1 gene by extending our observations made from the blood sample of one individual to a panel of normal and affected tissues. The 5' region of the gene, that has been difficult to study, will be surveyed for additional splicing variants using unique reagents developed by the applicant. The physiologic significance of alternative transcripts will then be assessed using a number of approaches including the generation of monoclonal antibodies quantitation of transcript expression levels and comparison of splicing patterns across species. The role of the gene's long polypyrimidine tract in generating the novel splicing pattern that we have described will be examined using well-characterized cell culture systems. Characterization of splicing will provide novel insights into the biology of the PKD1 gene and will have important implications for investigators developing RNA based tests for this disease.